Why is Bash not evaluating the executable bit correctly in Alpine 3.14.2?

In a dockerized Alpine 3.14.2 running Bash 5.1.4(1), I encountered a strange behaviour in a Bash script. The essential line is a test for executability of a file, which always fails. This is the if test in a nutshell:

bash-5.1# if [ ! -x /opt/java/openjdk/bin/java ]; then echo "something strange just happened"; fi
something strange just happened

But, the numerous ways I know of to "test" executability all show a different result:

bash-5.1# ls -la /opt/java/openjdk/bin/java
-rwxr-xr-x    1 root     root         12648 Jan 21  2021 /opt/java/openjdk/bin/java
bash-5.1# stat -c "%A" /opt/java/openjdk/bin/java
-rwxr-xr-x
bash-5.1# /opt/java/openjdk/bin/java --version
openjdk 15.0.2 2021-01-19
OpenJDK Runtime Environment AdoptOpenJDK (build 15.0.2+7)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 15.0.2+7, mixed mode, sharing)

In order to get my script working, the executability test inside Bash should return the proper result. But why doesn't it?

There is a rather long list of things I checked or tried out, some of them after suggestions from the community:

• The check fails all (tested) executables. Even Bash itself. The result is always wrong:

bash-5.1# if [ ! -x /bin/bash ]; then echo "this is weird"; fi
this is weird

• @KamilMaciorowski suggested to test for bash overrides in his comment. But the output seems fine:

bash-5.1# type -a [
[ is a shell builtin

• This is a strace on the command (thanks @zevzek):

bash-5.1# strace -fe trace=access,faccessat,stat bash -c '[ -x /bin/bash ]'
stat("/root", {st_mode=S_IFDIR|0700, st_size=4096, ...}) = 0
stat(".", {st_mode=S_IFDIR|0700, st_size=4096, ...}) = 0
stat("/root", {st_mode=S_IFDIR|0700, st_size=4096, ...}) = 0
stat("/root", {st_mode=S_IFDIR|0700, st_size=4096, ...}) = 0
stat(".", {st_mode=S_IFDIR|0700, st_size=4096, ...}) = 0
stat("/usr/local/sbin/bash", 0x7ffc257ec050) = -1 ENOENT (No such file or directory)
stat("/usr/local/bin/bash", 0x7ffc257ec050) = -1 ENOENT (No such file or directory)
stat("/usr/sbin/bash", 0x7ffc257ec050)  = -1 ENOENT (No such file or directory)
stat("/usr/bin/bash", 0x7ffc257ec050)   = -1 ENOENT (No such file or directory)
stat("/sbin/bash", 0x7ffc257ec050)      = -1 ENOENT (No such file or directory)
stat("/bin/bash", {st_mode=S_IFREG|0755, st_size=760136, ...}) = 0
stat("/bin/bash", {st_mode=S_IFREG|0755, st_size=760136, ...}) = 0
+++ exited with 1 +++

• Using the "real" [ from Busybox works fine, but not using [ in Bash. But I can't possibly rewrite all Bash scripts shipped with software in that container:

bash-5.1# which [
/usr/bin/[
bash-5.1# if [ ! -x /bin/bash ]; then echo "this is weird"; fi
this is weird
bash-5.1# if /usr/bin/[ ! -x /bin/bash ]; then echo "this is weird"; fi
bash-5.1#

• The filesystem is not mounted "noexec" (only the ones you would expect, like /proc)

• Other tests like [ -f /bin/bash ] or [ -f /tmp/not_there ] are correct, only -x seems broken

• I tried Bash 5.1.1 and it worked there. I then went through the Bash release notes, but I can't find anything relevant in between.